(1) Field of the invention
The present invention relates to a device for temporarily retaining a plurality of relatively movable chuck jaws in a predetermined relative position. The device according to the invention is particularly adapted to block the jaws of a chuck in a desired working condition at which their clamping surfaces may be ground true, i.e. the surfaces of the head portions of the jaws which grip the workpiece therebetween are accurately positioned for a grinding operation, in order that said surfaces are ground true with respect to the workpiece that is to be supported therein. The device according to the invention is particularly adapted for retaining in a predetermined position the chuck jaws which are made completely of hard steel, and do not present a mild-steel jaw insert.
(2) Prior art devices
There are known retainer devices which are used for retaining in position the composite jaws of a chuck, i.e. the jaws which present a support portion made of hard steel onto which there is changeably mounted a gripper portion, or clamping head portion. The gripper portion directly comes into contact and engages the workpiece to be positioned on the chuck. This gripper portion is made of mild steel (or any other metal which can be easily machined). The mild-steel gripper portion of the jaw is usually made in the form of a jaw insert which presents frontal bores which can be engaged by locking pins provided on blocking slides radially movable on a carrier ring which is positioned frontally with respect to the chuck. The locking pins of this prior art arrangement are set at a predetermined relative position and lock the jaws (through the engagement with the bores provided in the mild-steel jaw insert) in a correspondingly predetermined relative position, after which the mild-steel jaw inserts can be machined, as by turning or grinding, as required for gripping the workpiece therebetween in an optimum manner.